The prior art describes a variety of useful, self-curing compositions that can be applied to human fingernails to form an artificial nail. In general, these compositions are two-part systems which consist of a liquid portion (herein referred to as a binder) and a powder portion (herein referred to as a polymeric powder). The liquid binder comprises the following ingredients:
(a) a monomeric acrylate or methacrylate ester such as ethyl methacrylate or tetrahydrofurfuryl methacrylate, and
(b) a di-, tri-, or multi-functional acrylate or methacrylate ester such as ethylene glycol dimethacrylate or 1,4-butanediol dimethacrylate, and
(c) a tertiary amine accelerator such as N,N-dimethylpara-toluidine.
Optionally, the liquid binders may be seen to obtain polymerization inhibitors, such as BHT, dyes, and light stabilizers.
The polymeric powder portion of the prior art compositions generally comprise the following ingredients:
(a) a polymeric methacrylate such as poly(ethyl methacrylate) or copolymeric methacrylate such as a 70/30 molar ratio poly(ethyl-co-methyl methacrylate), and
(b) a perioxide polymerization initiator such as benzoyl peroxide.
Optionally, these polymeric powder portions may contain pigments, such as titanium dioxide, secondary polymers, such as poly(vinyl acetate) and flow modifiers such as fumed silica.
The practice of forming an artificial fingernail in situ (i.e., on a human fingernail) is a very exacting art. An artist's-type brush is first dipped in a reservoir containing the liquid binder portion, then transferred to a reservoir containing the polymeric powder portion. The wetted brush is allowed to contact the polymeric powder in such a way as to absorb sufficient powder to form a dough-like mass at the end of the brush. This dough is transferred to the surface of the human fingernail and subsequently shaped with the brush to form the desired coating and/or artificial fingernail extension. In the process of mixing the liquid binder with the polymeric powder a free-radical polymerization process is initiated by the combination of the peroxide (in the polymeric powder portion) with the tertiary amine (in the liquid binder portion). The proper balancing of initiator and accelerator, and liquid binder and polymeric powder, allows sufficient working time to shape the desired artificial fingernail before the dough like mass polymerizes to a hard, fused plastic. The curing time is generally from about 60 seconds to about 240 seconds from the time of initial mixing of liquid and powder.
A critical parameter in the formulation of artificial fingernail compositions is the consistency of the abovedescribed dough-like mass that is formed on the artist's brush. A consistency that can be easily moved and shaped with the brush, yet does not slump or sag is considered ideal. The key to achieving such working properties lies in the correct matching of liquid binder components with polymeric powder components. The liquid binder must display sufficient solvency properties in order to dissolve, or at least partially dissolve the polymeric powder. The converse must also be true; that the polymeric powder must be selected such that it is soluble or at least partially soluble in the liquid binder to achieve the desired consistency of the dough-like mass.
Variables that can be adjusted in the polymeric powder portion include choice of polymer or copolymer used (molecular weight of polymer, ratio of chain elements in a copolymer, etc.), particle size distribution of the polymer powder, and inclusion of flow modifiers in the polymeric powder portion. The liquid binder portion can be varied as to its's solvency properties for a given polymeric powder, and this, in turn, is based on the particular choice of monomeric acrylates and/or methacrylates for the liquid binder.
There has been much concern recently in the artificial fingernail industry over the potential toxicity from inhaling the monomeric acrylates and/or methacrylates utilized in the liquid binder portion of these compositions. Accumulation of monomer vapors in the workplace is certainly cause for concern, and is obvious to any nail technician due to the strong odors given off by most of the liquid binders that are available commercially.
Prior art compositions are based on liquid binders that contain monomeric acrylates and/or methacrylates with easily detectable odors. In addition, the inclusion of acrylate monomers (in addition to di-, tri-, and multi-functional acrylates) is considered a toxicological hazard in compositions intended for human contact. Thus, it would be advantageous to formulate a liquid binder with very little or no detectable odor that retained the correct working properties for making artificial fingernails.
Relevant prior art compositions are described in U.S. Pat. Nos. 3,539,533, 4,104,333, 4,058,442, 4,229,431, and 4,260,701. The acrylate and/or methacrylate monomers that are the subject of these inventions have distinctly detectable odors or have toxicity profiles that preclude their use for cosmetic applications. Particularly relevant is U.S. Pat. No. 4,260,701, which describes compositions useful for making artificial fingernails which are comprised of a major portion of methoxyethyl methacrylate. While methoxyethyl methacrylate possesses a mild, characteristic odor, recent studies have shown that there is a risk that the ethylene glycol monoether methacrylates of this kind may cause of possible birth defects. Similarly, ethoxyethyl methacrylate and butoxyethyl methacrylate fall into this same class of compounds and are toxicologically unsuitable for compositions intended for human contact.